When there is no data communication for a wireless local area network (WLAN) communications module, a station enters a power saving state, that is, the WLAN communications module is disabled. No data communication may mean that the station neither receives a data frame or a management frame sent by another station (for example, an access point (AP)), nor needs to transmit a data frame or a management frame. Before the WLAN communications module is disabled, the station sends a null data frame including a power saving tag to the access point, to notify the access point that the station has entered the power save mode. The power saving tag in the null data frame is set in a Power Management bit in a Frame Control field. When the bit is 1, it indicates that the station is in the power save mode.
After receiving the null data frame including the power saving tag, the access point knows that the station has entered the power save mode, and does not directly send a data frame to the station, but first wakes up the station and then sends the data frame to a terminal. However, the access point not only receives and sends a data frame on an operating channel, but also needs to temporarily switch from the operating channel to another channel. The operating channel is a channel used for current data frame transmission. If the access point is using the another channel when the station sends the null data frame including the power saving tag to the access point, the access point cannot receive the null data frame that includes the power saving tag and that is transmitted on the operating channel. Because the access point does not know that the station has entered the power save mode, the access point sends a data frame to the station as usual. In this case, the data frame is lost.